Many coffeehouses are nonprofits. Many schools require that students do some kind of public service. That could include volunteering at a coffeehouse. They can do any of the work involved, from setting up and putting away chairs to being trained to work a soundboard and then doing that.

Bring in younger performers who promote themselves heavily on social media. Local performers who show promise could do short opening sets. Their family and fans should show up. Hopefully some of them will stay for the rest of the evening and come back again.